The present invention relates to the field of antennas, and, more particularly, to a phased array antenna.
Phased array antennas are well known, and are commonly used in satellite, electronic warfare, radar and communication systems. A phased array antenna includes a plurality of antenna elements and respective phase shifters that can be adjusted for producing a focused antenna beam steerable in a desired direction.
A scanning phased array antenna steers or scans the direction of the RF signal being transmitted therefrom without physically moving the antenna. Likewise, the scanning phased array antenna can be steered or scanned without physically moving the antenna so that the main beam of the phased array antenna is in the desired direction for receiving an RF signal. This enables directed communications in which the RF signal is electronically focused in the desired direction.
Unfortunately, phased array antennas are limited in their application primarily by cost. Even using the latest monolithic microwave integrated circuit (MMIC) technology, an individual phase shifter may have a unit cost in excess of $500. With a typical phased array antenna requiring several thousand antenna elements, each with its own phase shifter, the price of the phased array antenna quickly becomes very expensive.
Attempts have been made to lower the cost of the antenna elements. One type of phase shifter includes switching diodes and transistors that change the path length, and thus the phase shift through the phase shifter via bias current changes.
Another type phase shifter includes a phase shifting material that produces a phase shift via a DC static voltage applied across the material. The dielectric properties of the phase shifting material change under the influence of a controlled voltage. A variable voltage applied to the phase shifting material induces a change in its dielectric constant. As a result, a signal being conducted through a transmission line connected to the phase shifting material exhibits a variable phase delay. In other words, the electrical length of the transmission line can be changed by varying the applied voltage.
For example, U.S. Pat. No. 5,694,134 to Barnes discloses a phased array antenna structure for controlling the beam pattern of a phased array antenna. A thin film of phase shifting material is deposited on the coplanar waveguide and/or the antenna elements. When a variable voltage is applied between the center conductor and the ground structure of the coplanar waveguide, a change in the dielectric constant of the thin film of phase shifting material is induced. As a result, the coplanar transmission line exhibits a variable phase delay.
However, a disadvantage of this approach is that it is difficult to adequately control the dielectric constant of the thin film of phase shifting material since the phase shifting material is adjacent the entire array as one continuous layer. The efficiency of the antenna is reduced since the thin film of phase shifting material increases the loss per unit length in the areas in which it is not phase shifting, i.e., between the phase shifting regions.
Moreover, the thin film is difficult to handle due to its limited thickness, which is several microns or less. The thin film of phase shifting material is typically deposited using evaporation, sputtering or laser beam ablation techniques. Depositing the thin film of phase shifting material using these types of deposition processes also adds to the cost of the phased array antenna. All of these effects result in the Barnes approach not being practical or affordable.
In view of the foregoing background, it is therefore an object of the present invention to provide a phased array antenna and a method for forming the same at a significantly lower cost than a conventional phased array antenna.
This and other advantages, features and objects in accordance with the present invention are provided by a phased array antenna comprising a plurality of antenna elements and a phase shifting device connected to the plurality of antenna elements. The phase shifting device preferably comprises a substrate, and a plurality of phase shifters on the substrate.
Moreover, each phase shifter preferably comprises a first conductive portion adjacent the substrate and defining a signal path, and a body adjacent the signal path and comprising a phase shifting material having a controllable dielectric constant for causing a phase shift of a signal being conducted through the signal path. The plurality of bodies are preferably laterally spaced apart from one another. The phase shifting material preferably comprises a ferroelectric material, such as barium strontium titanate, or a ferromagnetic material.
In one embodiment, the body preferably comprises a substrate with a layer of the phase shifting material thereon. In another embodiment, the body preferably comprises a bulk phase shifting material body.
The body preferably has an overall thickness equal to or greater than about 0.002 inches. Because the body has a thickness that is relatively easy to handle, it is simply bonded to the signal path in the appropriate place to define a phase shifter. Consequently, instead of individually building the phase shifters and combining them together to form the phased array antenna, the phased array antenna may be built in its entirety by forming the signal paths on the substrate and then bonding the bodies thereto. This advantageously allows low loss transmission media to be used to form the beam combiner and phase shifting material only in the phase shifting regions. In other words, the phased array antenna according to the present invention may be scaled and formed in any desired size, for example.
In forming the phased array antenna, the body is preferably loaded into production surface mount or similar machines. This allows construction of a much lower cost phased array antenna. The present invention is thus very adaptable to mass production using bulk phase shifting material body fabrication techniques.
The phased array antenna may further comprise a summing network connected to the phase shifting device for adding together the signals from the antenna elements. In addition, the phased array antenna may further comprise a beam forming network connected to the phase shifting device for controlling a voltage applied to each body for controlling a respective dielectric constant thereof.
Each phase shifter preferably further comprises at least one second conductive portion adjacent the substrate for defining a ground structure. In one embodiment, the at least one second conductive portion preferably comprises a pair of laterally spaced apart second conductive portions adjacent the substrate and on opposite sides of the signal path. This defines a coplanar waveguide structure. The body is also preferably further adjacent the pair of second conductive portions. In another embodiment, a second conductive portion is vertically spaced from the signal path. This defines a microstrip structure.
Another aspect of the invention relates to a method for making a phase shifting device comprising a substrate and a plurality of phase shifters on the substrate. The method preferably comprises forming a plurality of first conductive portions adjacent the substrate for defining a plurality of signal paths, and positioning a plurality of bodies adjacent the plurality of signal paths.
The plurality of bodies are preferably laterally spaced apart from one another and comprises a phase shifting material have a controllable dielectric constant for causing a phase shift of a signal being conducted through a respective signal path. Positioning each body may be performed using a surface mount machine. Each body may have a thickness equal to or greater than about 0.002 inches.